In U.S. patent application, Ser. No. 09/613,989, a method is disclosed that enables the use of paper or textured media to be authenticated based upon an embedded signal derived from the physical textural attributes of the media. A carrier is formed by scanning a region or multiple regions of the media and is convolved with a message to form an authenticable signal. After scanning, the carrier is subdivided and rearranged in ways that prevents a person from “discovering” the carrier.
Although this method is satisfactory, it includes drawbacks. One such drawback is that it adversely affects the robustness of the data-embedding algorithm. When the receiver having the carrier is being verified as authentic, the carrier regions must be rescanned. Any scanning errors introduced, for example, in scanning angle, in scanning starting point, or in scanning scale are compounded proportionately to the number of subdivisions, mirrors or other manipulations applied to improve security. These errors affect the algorithms robustness or equivalently the data capacity of the algorithm.
Consequently, a need exists for a means to either completely overcome the errors introduced by the rescanning process or to minimize their effect while improving overall security of the processes.